Model-based Methods for Web Service Verification

Outline PAT Introduction and Demo Overview of Web Services (WS) –Two views of WS –Problems addressed WS Modeling Languages WS Verifications Experiments Conclusion and Future Works

PAT: Process Analysis Toolkit PAT is a SPIN-like self-contained environment for system specification, visualized simulation and automated verification.

Two Views of Web Services Web service choreography describes collaboration protocols of cooperating Web service participants. –A global point of view –A contract among multiple corporations, i.e., a specification of requirements –May not be executable –WS-CDL (Web Service Choreography Description Language) Web service orchestration is the automated arrangement, coordination, and management of (external) Web Services at the message/execution level –A local point of view –An orchestration is the composition of concrete services provided by each corporation who realizes the contract. –Executable –WS-BPEL (Web Service Business Process Execution Language)

Problems Addressed Verification –Whether a choreography or an orchestration is correct with respect to critical system properties Deadlock-freeness Reachability testing Temporal logic formulae (LTL) –Whether they are consistent with each other the orchestration faithfully implements all and only what the contract states. Synthesis –to decide whether a choreography can be realized faithfully by any orchestration (refereed as implementable) and –synthesize a prototype orchestration if possible.

WS Module Workflow

WS Modeling Languages Intermediate modeling languages for Web services –Languages like WS-CDL or WS-BPEL are designed for machine consumption and therefore are lengthy and complicated in structure –Mismatches between WS-CDL and WS-BPEL –Intermediate languages focus on the interactive behavioral aspect –Our verification and synthesis approaches is not bound to one particular Web service

Choreography Language

Online Shopping Example

Semantic Model for Choreography A system configuration is a 2-tuple (I,V) –I is a choreography and V is a mapping from the variables to their values Labeled Transition System (LTS) is (S,init,T) –S is the set of reachable configurations, –init is the initial state (i.e., the initial choreography and the initial valuation of the variables) and –T is a labeled transition relation defined by the semantics rules. –Transition –Execution –Single Trace –Traces

Orchestration Language

Online Shopping Example

Verifications Deadlock-freeness Reachability testing Temporal logic formulae (LTL) Conformance Checking –An orchestration O is valid implementation of a choreography I if and only if O refines I, i.e., traces(O) ⊆ traces(I)

Conformance Checking Algorithm

Experiments

Conclusion A model-based methods for fully automatic analysis of Web service compositions –Intermediate languages –Verification –Synthesis (light-weight) Future Works –Language enrichment Event handlers, fault handlers and compensation handlers. –To support more Web service composition language, e.g., Orc language. –Automatic conversions between WS-BPEL/WS-CDL and our language –Optimization techniques Candidates include those which are designed for parameterized systems and infinite state systems